Problem: $\dfrac{2}{10} + \dfrac{10}{100} = {?}$
Solution: The fractions must have the same denominator before you can add them. Rewrite $\dfrac{2}{10}$ as $\dfrac{20}{100}$ $\dfrac{20}{100} + \dfrac{10}{100} = {?}$ $ = \dfrac{30}{100}$